To explore the clinicopathological characteristics of breast cancer patients with bone metastasis, and analyze their prognosis and related influencing factors.

According to the inclusion and exclusion criteria, totally 5 815 patients with metastatic breast cancer from January 1975 to December 2016 were screened out from the Surveillance, Epidemiology and Results (SEER) database of the U. S. National Cancer Institute for a retrospective analysis. The clinicopathological characteristics, treatment methods and prognosis of patients were evaluated. Among them, there were 3 146 patients with bone metastasis and 2 669 without. According to their prognosis, 3 146 patients with bone metastasis were divided into two subgroups: 1 669 patients in the death group and 1 477 patients in the survivor group. The χ² test and Mann-Whitney U test were used to compare the clinicopathological characteristics between bone metastasis group and non-bone metastasis group, binary Logistic regression was used to analyze the influencing factors of bone metastasis in breast cancer, the Kaplan-Meier method was used for survival analysis. The univariate log-rank test was used to analyze clinicopathological characteristics between the dead cases and survivors in 3 146 patients with bone metastasis, and the multivariate Cox proportional hazards regression model was used to find risk factors affecting the survival of patients.

There were significant differences in T stage, N stage, pathological grade, race, ER, PR, HER-2, molecular subtyping and prognosis between the bone metastasis group and non-bone metastasis group (Z=-5.71, -2.39, -13.87, χ²=14.55, 305.74, 245.56, 69.34, 335.36, 79.15, all P<0.050), while patient age, gender and position of primary tumor presented no significant difference (χ²=0.57, 2.71, 0.45, all P>0.050). The result of Logistic regression analysis showed that ER positive, PR positive, advanced T stage and advanced N stage were independent risk factors of bone metastasis in breast cancer patients(OR=1.775, 95%CI: 1.258-2.505, P=0.001; OR=1.425, 95%CI: 1.236-1.643, P<0.001; OR=1.095, 95%CI: 1.043-1.149, P<0.001; OR=1.396, 95%CI: 1.246-1.564, P<0.001), while advanced pathological stage indicated lower risk of bone metastasis (OR=0.815, 95%CI: 0.733-0.907, P<0.001). The overall survival showed a significant difference between the bone metastasis group and non-bone metastasis group (χ²=133.53, P<0.001). In patients with bone metastasis, there were significant differences in T stage, N stage, pathological grade, patient age, ER, PR, HER-2, molecular subtyping, primary tumor surgery, chemotherapy and radiation therapy between death group and survivor group (Z=-7.75, -3.22, -8.14, χ²=39.80, 69.81, 87.45, 51.87, 132.47, 36.24, 6.05, 36.24, all P<0.050). The multivariate analysis of Cox proportional hazards model showed that patient age, T stage, N stage, PR, HER-2, molecular subtyping, pathological grade, chemotherapy, radiotherapy and primary tumor surgery were independent factors affecting the prognosis of breast cancer patients with bone metastasis(HR =1.349, 95%CI: 1.195-1.523, P<0.001; HR=1.151, 95%CI: 1.101-1.203, P<0.001; HR=1.077, 95%CI: 1.033-1.123, P<0.001; HR= 0.715, 95%CI: 0.626-0.817, P<0.001; HR=0.695, 95%CI: 0.627-0.770, P<0.001; HR=1.349, 95%CI: 1.260-1.414, P<0.001; HR=1.371, 95%CI: 1.261-1.489, P<0.001; HR=0.626, 95%CI: 0.562-0.697, P<0.001; HR=0.874, 95%CI: 0.791-0.966, P=0.008; HR=0.663, 95%CI: 0.561-0.784, P<0.001).

The prognosis of breast cancer patients with bone metastasis is superior to that of the patients with non-bone metastasis, related to patient age, T stage, N stage, PR, HER-2, molecular subtyping and pathological grade. Primary tumor surgery, radiotherapy and chemotherapy can significantly improve the prognosis of patients with bone metastasis.